Having spent the last week at PDC - with very spotty Internet access. I thought I'd take some time to reflect on what I thought about the various announcements and technologies that I dug around in. This post is about the big announcement: Windows Azure

Azure (apparently pronounced to rhyme with badger) is an infrastructure designed to control applications installed in a huge datacenter. Microsoft refer to it as a “cloud based operating system” and talk about it being where you deploy your apps for Internet scale.

So I guess we have to start with: what problem are Microsoft trying to solve? There are two answers here:

1)Applications that need Internet scale are really hard to deploy due to the potentially huge hardware requirements and cost of managing that infrastructure. Most organizations that go through rapid growth experience a lot of pain as they try to scale for the 10,000s to many millions of users (Pinku has some great slides on the pain MySpace went through and how they solved it). This normally requires rearchitecting of the app to more loosely couple, etc.

2)Microsoft have a serious threat from both Amazon and Google in the high scaling world as both of those companies already have “cloud solutions” in place. They had to do something to ensure they were not left behind.

So Microsoft started the project to create an infrastructure to allow customers to deploy applications into Microsoft’s datacenter that would seamlessly scale as their requirements grew – Azure is the result.

The idea then is that you write your software and tell Microsoft what facilities you require – this is in the form of a manifest config file: “I require 20 instances of the web front end and 5 instances of the data processing engine”. The software and config is then deployed in to Microsoft’s infrastructure and a component called the Fabric Controller maps the software on to virtual machines under the control of a hypervisor. They also put a load balancer in front of the web front end. The web site runs as a “web role” that can accept requests from the Internet and the processing engine gets mapped to a “worker role” that cannot be accessed externally.

The Fabric Controller has responsibility to ensure that there are always a number of running instances your components even in the face of hardware failures. It will also ensure that you can perform rolling upgrades without taking your app offline if that what you require.

The problem that apps then face is that even though they may run on a specific machine at one point, the next time they are initialized they may be on a completely separate machine and so storing anything locally is pointless apart from as a localized cache. That begs the question: where do I store my state? Enter the Azure Storage Service. This is a massively scalable, fault tolerant, highly available storage system. There are three types of storage available

Queue: queue based data for storing messages to be passed from one component to another in the azure infrastructure

Hopefully Blob and Queue are fairly familiar constructs to most people. Table probably needs a little clarification. We are not talking about a relational database here. There is no schema for the table based data so, in fact, every row could be shaped completely differently (although this would be pretty ugly to try to read back out again). There are no relations and therefore no joins. There are also no server managed indexes – you define a pseudo index with the idea of a partition ID – this ID can be used to horizontally partition the data across multiple machine clusters but the partition ID is something you are responsible for managing. However, each row must be uniquely identifiable so there is also a concept of a row id and the partition id/row id combination make up the primary key of the table. There is also a system maintained version number for concurrency control. So this is where the strange number of 252 user defined properties comes from 255 – 3 (partition id, row id, version)

So in the above example, the web front end passes the data processing engine the data by enqueing it into queue storage. The processing engine then stores the data further (say in a blob or table) or just processes and pushes the results back on another queue. It can also send messages out to external endpoints.

All components run under partial trust (a variant similar to ASP.NET medium trust) so Azure developers will need some understanding of CAS.

The API for talking to Azure is REST based which can be wrapped by ADO.NET Data Services if appropriate (e.g. for table storage)

To get started you need an account provisioned (to get space reserved in the datacenter). You can do this via http://www.azure.com. There are other services built on top of Azure, which I will cover in subsequent posts, which get provisioned in the same place.

There is an SDK and VS2008 SP1 integration. This brings a development fabric to your machine that has the same services available as the cloud based one so you can test without deploying into the cloud. There are also VS project templates which in fact create multiple projects: the application one(s) and another to specify the deployment configuration.

So where does that leave Microsoft. They have created an offering that in its totality (which is much more than I have talked about here) is beyond what both Amazon and Google have created in terms of functionality. But they are left with two issues:

1)Will companies trust Microsoft to run their business critical applications? Some definitely will but others will reserve judgement for some time until they have seen in practice that this infrastructure is sound. Microsoft say they will also have an SLA in the contract that will have financial penalty clauses if they fail to fulfil it in some currently unspecified way

2)Microsoft have not yet announced any pricing model. This leaves companies in a difficult position – do they throw resources at a project with a lot of potential and bear the risk that when Microsoft unveil the pricing their application is not economically viable? Or do they wait to start investing in this technology until Microsoft announce pricing. Unfortunately this is a chicken and egg situation – Microsoft cannot go live commercially until the infrastructure has been proven in practice by companies creating serious app on it, and yet they do not want to announce pricing until they are ready for commercial release. Hopefully they will be prepared to discuss pricing for any organization that it serious about building on the infrastructure on a case by case basis before full commercial release.

Azure definitely has huge potential for those companies that need a very flexible approach to scale or who will require scale over time but that time cannot yet be determined. It also has some challenges for how you build applications - there are design constraints you have to cater for (failure is a fact of life and you have to code to accept that for example).